Kazuul's Fury // Kazuul's Cliffs

The two faces solve two different problems, and the split is the point. The spell half is flood insurance: once you have drawn enough lands, it converts a body's death into reach, cashing in a creature's power as damage to any target at the exact moment it was going to die anyway (to a sweeper, to a block it will not survive, to a sacrifice loop that already wanted it in the graveyard). Sacrificing the creature is what keeps that reach from being free; you are paying with a body, not conjuring damage from nothing. Instant timing is the real lever. A creature declared as an attacker can be thrown for its full power at any point before combat damage, redirecting that value from the blocker it was trading with to a face or a planeswalker instead. A creature targeted by removal can be turned into its own worth in response. Against a one-mana sorcery like Thud that does similar work, the extra cost buys the ambush window: the ability to hold the throw until an instant-speed opening appears. The land back is the flip side of that bargain, screw insurance for the early game: a red source that enters tapped but costs only a slot, so a hand light on lands can still make its drops and the spell half never has to be a card you regret drawing.